DESCRIPTION: Amyloidosis, a disorder of protein metabolism identified by extracellular deposition of fibrils, is associated with aging and/or plasma cell dyscrasias like multiple myeloma. Tissue destruction, cell loss and pain are the inevitable results of amyloid accumulation. Immunoglobulin light (L) chains are the most common precursors of fibrils (AL amyloidosis). The principle aims of this proposal are to enlarge the database of three-dimensional structures of amyloidogenic antibody proteins, or fragments therefrom, and to determine the general features of the protein precursors of amyloid fibrils, and identify what makes them so destructive. Since the principal investigator has solved the crystal structures of seven conformational isomers of a l-type L chain from a patient (Mcg) with amyloidosis, it will serve as the prototypic amyloidogenic protein to model self assembly of precursors into fibrils. The structures of two additional amyloidogenic L chains, one l- and one k-type, will also be determined by X-ray crystallography and compared with the Mcg prototype. Heterologous (hybrid) dimers of Mcg and other L chains can be engineered to give structures and binding properties distinctly different from their progenitor molecules, but will also provide information about common intermolecular association motifs. Immunoglobulin heavy (H) chains can also be involved in amyloid formation (AH amyloidosis). However, in two immunoglobulins included in this study (Mcg IgG1 and Yvo IgM) the H chains caused different types of pathology. Their variable (VH) domains contributed to the formation of intravascular aggregates which in turn led to hyperviscosity and petechiae. Even when degraded with enzymes, the VH domains yielded peptides that were insoluble in aqueous solvents. Sequencing of the Mcg VH required innovative use of detergents and polyacrylamide gels, technology which will now be transferred to the Yvo VH problem. These sequences are essential for completing the X-ray analyses of the intact Mcg IgG1 and the Yvo antigen binding fragment (Fab).